1. Field of the Invention
The present invention relates to a video compression coding apparatus utilized for video data transmission and recording and to a video compression recording/playback apparatus for recording and play back video data on a highly efficiently compressed form.
2. Description of the Related Art
Conventionally, upon transmission, video data is often transmitted on a compression-coded form in view of the limited capacity of data transmission on a transmission circuit line and a cost involved. Even on the video recording apparatus, video data is sometimes recorded on a compression coded form in view of the cost, etc., of a recording medium.
In such a conventional video compression coding apparatus for performing compression coding process on the video data, control is effected to make a code quantity per unit time constant so as to correspond to the capacity of the transmission circuit line or of a recording medium.
In a practical application, if more code quantity is involved for a target code quantity, the video quality, that is, a quantization level is lowered to decrease the code quantity, while, on the other hand, if less code quantity is involved in that situation, the video quality, that is, the quantization level is enhanced to increase the code quantity.
At that time, the code quantity varies in accordance with the control of the quantization level. The code quantity levels, on the average, are fitted to the target code quantity and it is possible to accommodate a variation of the code quantity with the use of a buffer memory which is provided at an output stage. By so doing, the code quantity, after being compressed, is prevented by the type of image from being varied so that the code quantity is maintained constant.
In the video compression coding apparatus for making the code quantity constant as set out above, the video quality varies greatly by the type of image.
In the conventional video compression recording/playback apparatus, on the other hand, much difficulty is encounted in varying the per-unit-time reading rate of a magnetic medium, such as a recording medium and, for this reason, video compression is carried out with the use of a recording data quantity of at least a given field or frame unit. In a such video compression system, however, the compression rate is too high with respect to a quantity of information in the type of image containing more high-pass components, thus sometimes producing an image degradation upon playback.